Grain refinement and superplasticity of Al-Mg alloy by hydrogenation treatment

The grain refinement is noticed as a method to enhance the strength of materials and to be appeared the superplasticity behavior. The magnesium element contained in Al-Mg alloy has characteristic properties such as hydrogen absorption and dehydrogenation at high temperature. Hydride precipitations MgH2 obtained in this treatment were more useful to develop the high-density dislocation structure in alloy as dislocations pileup sources The details of the fabrication process of grain refinement technique and an effect of the hydrides on mechanical properties of material, especially, superplasticity of fine grained Al-Mg alloy to which dehydrogenation treatment was applied, were investigated. This paper presents the possibility of gain refinement of A-W alloy to occur utilizing this phenomenon. A hydrogenated material which has 1.06 mass% of hydrogen content using heavy cold tolling with the 90% reduction ratio to induce high stored strain energy was heated to have rapid recrystallization in salt bath. It was found that the microstructure bad an average grain size of 20 mum and this size decreased with the increasing of the hydrogen content. It was also found that this hydrogenation treatment was an effective technique for grain refinement For Al-Mg alloy with these treatments, yield strength increased more than IS times in comparison with that of untreated material. About 300% elongation was obtained at 625 K and 5x10(-3) s(-1) strain rate.